Differences in the confluence of mesial canals in mandibular molar teeth with three or four root canals

To investigate the correlation between number of root canals and their confluence in mandibular molar teeth.

A total of 553 first and 383 second mandibular molars were root filled between the beginning of 1997 and the end of 2006. Access cavities were prepared and the pulp chamber floors were carefully inspected with an endodontic explorer under magnification of 4x. After negotiating the root canal system, the 'straightest' canal of each root was instrumented. A gutta-percha cone was placed in the canal and a small file (08 or 10) was inserted to working length and then removed in all other canals. The gutta-percha cone was removed and inspected for notches indicating the presence of confluences. If it was not possible to probe completely one or more canals, the canal confluences were classified as 'not determined' (ND) if there was no sign of confluence; if a notch was present canals were considered confluent. For each tooth, the number of root canals and the presence of confluences were recorded. To test whether there was a difference in frequency of confluences between teeth with three and four root canals the chi-squared analysis with Yates' continuity correction was performed.

The frequency of a confluence in mesial canals of first molars was 56% in teeth with three root canals and 34% in teeth with four canals. In second molars, it was 67 and 41%, respectively. Differences in the frequency of confluences in teeth with three and four root canals were statistically significant both in first and in second molars.

A greater incidence of confluent canals occurred in teeth with three rather than with four root canals both in first and second mandibular molars.